Well Unloading Solution - Winning Poster

H a s a n S i d d i q u i a n d J u l i u s M o n iGLNG Upstream Operations – Engineering & Planning, Santos Ltd, Brisbane, QLD 4000, Australia

W E L L U N L O A D I N G S O L U T I O N

Fairview is located in the Comet Ridge Project Area.Sales gas production commenced in 1997, and todayproduction is around 130 TJ/day, with the averagewell productivity at 1 TJ/day. Almost 200 wells havebeen drilled to date, and these wells are in variousstages of development. Longer term, more than 4,000wells will be required to feed gas to the LNG trains atGladstone.The coal seam gas field comprises of free-flow andpumped wells. A well consists of a separator, withwater and gas gathering lines. The gas flows toplants where it is compressed and dehydrated, whilethe water flows to treatment plants where it is treatedand recycled.During early stages of the well production life cycle,gas rates increase and water rates decrease. Waterproduction is the primary focus initially in thedewatering phase, as it allows the gas to flow later.

Wells that are able to flow gas above a “criticalvelocity” are able to lift water without intervention.Critical velocity is defined as the minimum gasvelocity in the tubing required to move liquid dropletsup to the surface.However some wells lose their ability to flow gasabove this “critical velocity”, for various reasons. Inthese wells, water builds up in the well bore (i.e. theyload-up). As wells load-up, it causes gas flow todecrease or cease, resulting in lost gas production.A tell tale sign of liquid loading is a significantdifferential pressure across the casing and tubingpressures on a free flow well. This is more typical inwells that are moving between the dewatering andstable phases of the production lifecycle.

IntroductionIntroduction Increasing bottom hole pressure is more expensive,as compared to decreasing the surface pressure. Forthis reason, decreasing the surface pressure is themore attractive option, and it is used in the design ofthe new well unloading solution.Additionally, by lowering the surface pressure (i.e. thebackpressure on the well) to atmospheric conditions,the maximum gas velocity is reached through thetubing, which creates the best conditions for liftingwater from the well bore.The skid assembly that we are constructing is mobileand will feature a separator that operates atatmospheric pressure.It is connected directly to the well head tubingminimizing backpressure. The separator will allow allgas to flow to the existing flare on the lease. Waterwill flow into unloading tank by gravity, minimizingenvironmental impact.Upon completion of unloading a tanker will removethe water and the equipment will be rigged down andmoved to the next candidate well.

Unloading Tank• 220 bbls capacity with access step and platform• Fully self contained in a single load, no crane

required for set up• Locally built in Roma, transport dimensions are

within restrictions of length, width, height, andweight

Design DetailsDesign Details

• Suits relatively simple needs of CSG wells• One truck for transport within road limits• All components are mounted on a single skid base• All components are easily handled and assembled

by a two-person work party• No automation is required• Designed to eliminate working at heights issue• Separator connection points to well and flare are

located on both sides of the skid• Gravity flow of water from separator to tank• Cost just under 200K, which can be recovered by

the production of one well in a year• Will be used to do simple well tests to determine

well completion requirements, which could savemore than 200K just for one well

AdvantagesAdvantages

Project UpdateProject Update• Concept design completed• Process design completed• Purchase order issued• Separator and tank design completed• 3D- Model completed and under review• Drafting in progress• Expected delivery date: End of year 2012

AcknowledgementsAcknowledgementsJames Jonutis – GLNG Upstream OperationsJessica McClintock – GLNG Upstream Operations

ReferencesReferencesJames F. Lea, Henry V. Nickens, and Mike R. Wells,Gas Well Deliquification

Separator Vessel• 2.2 MMscf/d and 400 bwpd capacity with manway,

internal ladder, and magnetic-type level gauge• Code & Class: AS 1210 & Class 2A• No PSV requirement, globe valve provides

pressure control at tie-in point

Connection to well

Connection to well Connections

to flareAimAim

ConceptConcept

The aim of the project is to develop a low costmethod to unload a well that provides predictable andrepeatable results in an environmentally friendly andcommercially viable way. Ideally, the new unloadingmethod should reduce well pressure to atmospheric,capture water and flare dry gas, all while eliminatingthe need for excavation, lining, fencing andremediation.

In order to restore water loaded wells to gasproduction, built up liquid is lifted from the well boreby increasing the gas flow velocity in the tubing. Thiscan be achieved by either:1. Increasing the bottom hole pressure by:

• Using an “air pack”; this uses a large compressorto pump a high volume of air down the annulusand unload the tubing against gathering systempressure

2. Decreasing the surface pressure to atmosphericconditions by:• bypassing the separator to the flare stack(banned)

• bypassing the separator to a flare pitAll the methods in the bullet points above have feweradvantages as compared to the disadvantages.Some of the disadvantages are: uncontrolled releaseof water to grade; expensive civil work; high potentialfor cold venting; expensive and unpredictable results.

When gas flow velocity from a well is not sufficient tolift the liquids to the surface against gathering systempressure, external intervention is needed to unloadthe well. At present in Fairview 10-20% of the existingwells require some form of treatment to unload thewell bore and reach maximum gas flow rates.

Time

Rate

Rate falling off decline curve, indication of loading

Declining water production curve analysis

time

dewatering stable decline

rates

Candidate CSG Wells